In order to increase the number of ICBMs that the SBI constellations discussed above could theoretically be capable of intercepting from a single missile to two missiles (without the assistance of a blissfully oblivious or self-destructive adversary), the number of SBIs in orbit would have to be doubled—with a commensurate increase in system costs of tens of billions of dollars. Worse yet, the additional increment of protection this would buy the United States could, in turn, be completely offset and undercut by the adversary's purchase of a single additional ICBM. And for a country that has already developed and produced an ICBM, additional missiles would likely cost no more than several tens of millions of dollars each to produce, and perhaps less. As a result, notwithstanding the enormous wealth of the United States relative to countries such as North Korea and Iran, this may not be a case where the United States could prevail by simply outspending its opponent.

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Kosiak, Steven M. Arming the Heavens: A Preliminary Assessment of the Potential Cost and Cost Effectiveness of Space-Based Weapons. Washington, D.C.: Center for Strategic and Budgetary Assessments, October 31, 2007. [ 19 quotes ] [ page 13-14 ]

 

According to the 2003 APS study of boost-phase ballistic missile defenses, the ABL would have a useful range against liquid fuel ICBMs of about 600 km, and would be capable of protecting the United States from a limited ICBM attack launched from North Korea, but incapable of defending against a similar attack from Iran, unless the United States could station ABLs over the Caspian Sea or Turkmenistan. However, the ABL's range against solid fuel ICBMs would be only about 300 km, insufficient to protect the United States from an ICBM launched from either North Korea or Iran. Moreover, as with other boost-phase ballistic missile defense systems, even where individual ICBMs could be successfully intercepted, salvo launches could prove difficult to handle. As the APS study notes, multiple ABLs might need to be deployed to defend against even a moderate number of multiple launches.

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Kosiak, Steven M. Arming the Heavens: A Preliminary Assessment of the Potential Cost and Cost Effectiveness of Space-Based Weapons. Washington, D.C.: Center for Strategic and Budgetary Assessments, October 31, 2007. [ 19 quotes ] [ page 31 ]

 

Among the most serious limitations of space-based boost-phase defense systems is the "abstentee" problem. Satellites in low earth orbit travel in their orbital plane at some 7–8 kilometers per second (km/sec). This means that a satellite in orbit at an altitude of 500 km, for example, will circle the earth once every 90 minutes. However, since the earth below is also spinning, the satellite will not travel above the same surface areas of the earth during each orbit. As a result of these dynamics, a space-based weapon will be within range of a particular location on the earth only a relatively small fraction the time. Because of this absentee problem, the only way to keep a particular spot on the earth continuously covered is to maintain a constellation of space- based weapons in orbit. The precise amount of time a space-based ballistic missile defense system will spend within range of a particular spot—and thus the total number of such satellites that will be needed to maintain continuous coverage—will depend on both the specific characteristics of the defensive system's orbit (e.g., its altitude and inclination) and the speed of its interceptor missile, or range of its laser.

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Kosiak, Steven M. Arming the Heavens: A Preliminary Assessment of the Potential Cost and Cost Effectiveness of Space-Based Weapons. Washington, D.C.: Center for Strategic and Budgetary Assessments, October 31, 2007. [ 19 quotes ] [ page 10 ]

 

Another problem inherent in boost-phase ballistic missile defense is that an intercept that successfully disabled a missile's booster would probably not result in the destruction the missile's warhead. An intercepted booster would rapidly lose thrust, but the ICBM's warhead, which is only loosely coupled to the final stage of the missile, along with booster fragments and other debris, would likely continue to fall to earth on a ballistic trajectory. The warhead would fall to the earth short of its intended target, but possibly in populated areas. And, if launched from North Korea or Iran, those areas would not be in the attacking country, but could be in the United States or another country.6 To ensure that an ICBM's warhead had not attained the velocity needed to reach the United States, it would be necessary to intercept the booster as early as 40 seconds before it would normally burnout.

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Kosiak, Steven M. Arming the Heavens: A Preliminary Assessment of the Potential Cost and Cost Effectiveness of Space-Based Weapons. Washington, D.C.: Center for Strategic and Budgetary Assessments, October 31, 2007. [ 19 quotes ] [ page 9 ]

 

Boost-phase defenses. The pursuit of a more effective missile defense, as envisioned by the Bush administration, would require space-based intercept components—such as the SBI and SBL—to catch missiles in their boost phase. As the recent report from the American Physical Society (APS) on boost- phase defense discussed, a number of countermeasures for SBI could be developed.103 One of the most potent countermeasures would be a fast-burn boost. Because it reduces the boost time by using solid-fuel, the fast-burn booster would make the job of a boost-phase interceptor defense extremely challenging or infeasible. The APS study concluded, "Switching from liquid- propellant to typical solid-propellant ICBMs would cut the boost phase by a minute or more. Boost phases as short as 130 seconds are certainly possible; such missiles would be practically impossible to intercept." As reported, China is developing solid-fuel ICBMs, and may be able to develop faster-burn rockets in the future. Other possible countermeasures include: lofting or de- pressing the trajectory of the ICBM relative to the maximum-range trajectory to evade attacks from space weapons; spoofing the defender's tracking sen- sors by deploying small, rocket-propelled decoys from the missile that mast or mimic the radar and electro-optical characteristics of the booster; and changing the brightness and configuration of the exhaust plume of the ICBM to make it more difficult for infrared sensors to locate the real missile body. For SBL, countermeasures could include: rotating the missile to distribute the laser energy from SBL over a wide area and protecting the vulnerable parts of the ICBM with reflective or ablative coatings.

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Zhang, Hui and Pavel Podvig. Russian and Chinese Responses to U.S. Military Plans in Space. Cambridge, MA: American Academy of Arts and Sciences, 2008. [ 16 quotes ] [ page 54 ]

 

Midcourse missile defenses. A number of countermeasures could feasibly defeat midcourse missile defense. Chinese scientists have followed and dis- cussed, for example, those countermeasures shown in the Union of Con- cerned Scientists/MIT report Countermeasures: A Technical Evaluation of the Op- erational Effectiveness of the Planned US National Missile Defense System.98 One efficient and simple countermeasure would be the deployment of decoys with each ICBM. Decoys can "confuse" the interceptor's sensors system, making it unable to discriminate between the real warhead and the decoys. The decoys might replicate the warhead or appear slightly different from one another and from the warhead. China might also disguise the warhead—a technique known as "antisimulation"—by enclosing it in a radar-reflecting balloon, cov- ering it with a shroud, hiding it in a cloud of chaff, or by using electronic or infrared jamming measures. These penetration aids, antisimulation and decoy technologies, are within China's capability.99 China has reportedly made some missile flight tests with penetration aids, such as the first flight test of China's new DF-31 ICBM, which included decoys, on August 2, 1999.100 China could also employ countermeasures to reduce the radar and in- frared signatures of the warhead, making detection more difficult. For exam- ple, China could reduce the radar cross-section of the nuclear warhead by shaping the reentry vehicle (or a shroud around it) as a sharply pointed cone and/or by coating it with radar-absorbing material. China could reduce the infrared signature of the warhead by covering it with a low-emissivity coating or by using a shroud cooled to low temperature by liquid nitrogen.

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Zhang, Hui and Pavel Podvig. Russian and Chinese Responses to U.S. Military Plans in Space. Cambridge, MA: American Academy of Arts and Sciences, 2008. [ 16 quotes ] [ page 54 ]